How much time to spend in Shanghai during layover

We arrive PVG at 10 a.m. and have to fly out at 9 pm same day. We would like to try Maglev train and see places in SH without compromising our flight back to US. Please let us know the immigration process we have to do and how long it would take to and from PVG. Our travel will be in the 2nd week of December. Thank you.